This invention relates to a polishing machine for polishing edges and portions near the edges of a target object by using a polishing tape and more particularly to such a polishing machine adapted to carry out the polishing by contacting the polishing tape to the target object without bending the polishing tape more than necessary.
A thin film is formed as shown in FIG. 10A on the surface of a target object to be polished such as a semiconductor wafer (indicated by letter W) but it is something to be removed because the thin film at beveled portions (indicated by letter B) along an edge or that on an edge section (indicated by letter E) on a circumference inside such a beveled portion tends to be a source of particles or contaminations of other forms. Particles are also likely to be generated from rough spots developed at beveled potions of a semiconductor device, depending on its production process, and it is coming to be considered necessary to improve the surface accuracy of portions from which a thin film has been removed.
For removing unnecessary portions of a thin film, it has been known to use the method of firstly forming a protective membrane on the surface of a semiconductor wafer and then to remove the film from beveled and edge portions by etching. Japanese Patent Publications Tokkai 2002-208572 and 2003-234314 have disclosed apparatus for removing a film from such places by using a polishing tape instead of by etching. By such an apparatus, an unnecessary membrane is removed by passing a polishing tape from the upper surface of a semiconductor wafer to an edge part and further down to the bottom surface and pressing it onto the semiconductor wafer by means of a polishing head.
Methods of removing a film from such a portion without using a polishing tape have also been developed, such as disclosed in Japanese Patent Publication Tokkai 2002-329687. By a method of removing a film by etching, on the other hand, there are situations where the etching rate becomes very slow such that the throughput becomes lower, depending on the kind of the film. Moreover, the apparatus must be resistant against chemicals that are used for the etching process, and the disposal of the waste liquid becomes necessary after the removal.
Use of a polishing tape does not accompany the kind of problems encountered when a film is removed by etching but the polishing tape must be bent to a significant degree in order to press it along the edge of a semiconductor tape because the thickness of the wafer is less than 1 mm.
Polishing tapes have a polishing layer containing a polishing material formed on a base sheet material. If such a polishing tape is bent excessively, the polishing layer comes to be separated and this generates particles and causes contamination.
If a polishing tape is bent in this manner as it is contacted to the edge portion of a semiconductor wafer, furthermore, it nearly becomes a point contact and the whole surface of the polishing tape cannot be effectively used for the polishing. If the width of the polishing tape is reduced in order to use it efficiently, it becomes easier to break and more polishing machines would be required for maintaining a high efficiency.
Polishing machines of the type not using any polishing tapes are adapted to use a dedicated special polishing material for removing a film at beveled and edge parts of semiconductor wafers and they have very complicated structures.
Japanese Patent Publications Tokkai 7-164301 and 8-174399 disclose polishing machines of the type having a polishing head that uses a polishing tape to polish end parts of a semiconductor wafer. Although they are adapted to rotatably support a semiconductor wafer, they cannot move in the perpendicular direction and hence cannot be used for polishing edge portions.